a. Field of the Invention
The present invention relates to the field of data compression and, more particularly, to a system and techniques for compressing digital motion video signals.
b. Related Art
Technological advances in digital transmission networks, digital storage media, very Large Scale Integration devices, and digital processing of video and audio signals are converging to make the transmission and storage of digital video economical in a wide variety of applications. Because the storage and transmission of digital video signals is central to many applications, and because an uncompressed representation of a video signal requires a large amount of storage, the use of digital video compression techniques is vital to this advancing art. In this regard, several international standards for the compression of digital video signals have emerged over the past decade, with more currently under development. These standards apply to algorithms for the transmission and storage of compressed digital video in a variety of applications, including: video-telephony and teleconferencing; high quality digital television transmission on coaxial and fiber-optic networks as well as broadcast terrestrially and over direct broadcast satellites; and in interactive multimedia products on CD-ROM, Digital Audio Tape, and Winchester disk drives.
Several of these standards involve algorithms based on a common core of compression techniques, e.g., the CCITT (Consultative Committee on International Telegraphy and Telephony) Recommendation H.120, the CCITT Recommendation H.261, and the ISO/IEC MPEG-1 and MPEG-2 standards. The MPEG algorithms have been developed by the Moving Picture Experts Group (MPEG), part of a joint technical committee of the International Standards Organization (ISO) and the International Electrotechnical Commission (IEC). The MPEG committee has been developing standards for the multiplexed, compressed representation of video and associated audio signals. The standard specifies the syntax of the compressed bit stream and the method of decoding, but leave considerable latitude for novelty and variety in the algorithm employed in the encoder.
Both the MPEG-1 and MPEG-2 algorithms can be described as hybrid transform encoding/motion compensation encoders. For an encoder to efficiently use motion compensation, it must perform a task called motion estimation. Also, motion estimation may be useful for rate control.
Motion estimation can be described in general terms as deciding where a particular region in a picture "came from" in a picture or pictures that occur temporal earlier or later in time and deciding how accurately a region of the current can be said to "come from" other pictures. If the encoder is comparing a single picture that occurs earlier or later in time then the current picture, we say that the encoder is doing unidirectional motion estimation. If the encoder tries to see how a region in the current picture "came from" more than one picture, we say that it is doing temporally interpolative motion estimation.
Motion estimation is one of the most computationally intensive tasks that an MPEG-1 or MPEG-2 encoder performs. Thus, an important consideration in building an MPEG-1 or MPEG-2 encoder is to use an economical motion estimation scheme.